The gas turbines used in electric power plants, nuclear power plants and various other industrial plants are velocity-type heat engines which employ as their operating medium their own operating gases, mainly air and combustion gases. These turbines basically comprise a compressor, which performs the adiabatic compression process; a combustor, which heats the air-fuel mixture under constant pressure; and a turbine, which performs the adiabatic expansion process.
The combustor has a number of combustion chambers, each with a tail pipe, in the space in the casing which is pressurized by the air from the compressor. The combustion gases generated in the combustion chambers are conducted via the tail pipes to the turbine, which they cause to rotate.
In this sort of combustor, the air pressurized by the compressor is conducted to the space in the combustor casing at all times. Since the amount of the pressured air for combustion is proportional to the state of combustion in the chambers (i.e., to the load fluctuation), and it fluctuates according to the state of combustion at all times, it is necessary to bypass the pressurized air in the space in the casing in order to maintain the air pressure at a constant level. In other words, a portion of the compressed air in the space is conducted via control valves or bypass channels into the tail pipes connected to the combustion chambers, mixed with the hot, high-pressure combustion gases in the pipes and released into the turbine, thus the pressure of the air in the space in the casing can be maintained at a constant level.
To be more specific, if the volume of air admitted to the bypass channels is controlled by a valve or a valve-adjusting mechanism, and a large volume of pressurized air is to be admitted to the combustion chamber, then the bypass valve can be constricted or closed by the valve-adjusting mechanism so that the volume of air flowing into the bypass channels is reduced or entirely cut off. If a small volume of pressurized air is to be admitted to the combustion chamber, the bypass valve can be opened more or opened all the way so that the volume of air flowing into the bypass channels is increased. In this way the air in the space in the casing can be maintained at a specified pressure.
The prior art design shown in FIG. 7 is a bypass air control device for controlling the volume of air which is bypassed. It consists of a control valve for the bypass channel and a mechanism for adjusting the valve.
4 is the pressurized space inside casing 7 of the combustor. In the space 4 under casing 7, a number of the combustion chambers (not shown) and the tail pipes 1 which are connected to them are arranged around the circumference of the casing. (In the drawing, only casing 7 and the essential portion of a single tail pipe 1 are shown.)
A bypass channel consisting of elbow pipe 3 and bypass pipe 2 is connected to the side of the tail pipe 1. Opening 2a at the front of the bypass channel faces space 4 in casing 7. Pressurized air can be bypassed into the tail pipe 1 via the opening 2a. A butterfly valve 5 is inside the bypass pipe 2. This valve controls the volume of air which is bypassed. Valve stem 19 of the butterfly valve 5 extends upward from the valve and is connected via a spline to adjustment shaft 17.
Shaft 17 is mounted to the outer surface of casing 7. Its operating portion is inserted through casing 7; its front end is connected via a spline to valve stem 19 of the butterfly valve 5.
Annular inner ring 9 is fixed on the outer periphery of the exterior (i.e., the upper surface) of the casing 7. The upper surface of the inner ring 9 is shaped into a rectangular depression. Shaft rollers 9a are mounted along the entire periphery of inner ring 9, so that outer ring 11 can freely move in contact with them in the bottom of the depression.
The bottom of outer ring 11 has a rectangular protuberance which engages in the shaft rollers in the inner ring 9 in such a way that it is free to rotate. The inner surface of the outer ring 11 and the upper end of adjustment shaft 17 are connected by link 13 and lever 15, which convert the rotational movement of the outer ring 11 to rotational movement of adjustment shaft 17.
Thus when outer ring 11 rotates in the peripheral direction with inner ring 9 as a guide, adjustment shaft 17 is caused to rotate via link 13 and lever 15.
Because adjustment shaft 17 is connected to valve stem 19 of butterfly valve 5 via a spline, the rotation of shaft 17 is linked to the rotation of valve stem 19, and valve body 21 of valve 5 can be made to open and close.
Thus the rotation in of outer ring 11 the circumferential direction on the outer surface of the casing 7 can be converted to a force which drives valve body 21 of butterfly valve 5 in bypass channel 2 and 3 within casing 7 to open or close. In this way it is possible to adjust the rate at which the air bypass control valve is opened, and with it, the volume of air which is bypassed.
In this sort of prior art air bypass device for controlling the volume of air, valve body 21 of butterfly valve 5 is made of a lightweight material, so vibration resulting from combustion could be transmitted via the tail pipe from the combustion chamber to the bypass channel. When this happened, the resonant vibration of the pipe would cause the valve body in the channel to stutter. This would result in greatly accelerated abrasion of the valve body, the shaft and the bearings for the valve stem in the bypass channel.